Soil Moisture Effects on Entomopathogenic Nematodes

Abstract

The effect of soil moisture on entomopathogenic nematode virulence was examined in the laboratory. Objectives were to determine the virulence of several species and isolates of entomopathogenic nematodes at various soil moisture contents and temperatures, and after ßuctuations in soil moisture. Studies included up to Þve isolates of entomopathogenic nematodes: Heterorhabditis bacteriophora Poinar (Oswego and Tuscarora strains), Steinernema glaseri (Steiner) (NC1 strain), S. feltiae (Filipjev) (Biosys 369 strain), and S. carpocapsae (Weiser) (NY001 strain). Nematodes were applied to sandy loam soils ranging in soil moisture content from below the permanent wilting point of plants to near saturation. In all experiments, a rainfall or irrigation event was simulated by adding water to rehydrate soils to high moisture levels (near saturation). Nematode virulence was evaluated periodically by measuring insect mortality in Galleria mellonella (L.) larval bioassays, before and after rehydration. Nematode virulence increased with soil moisture content for all species and isolates tested. Our studies demonstrated that the virulence of entomopathogenic nematodes in low moisture conditions could be restored by rehydrating the soil. Insect mortality was generally low in lowmoisture, nematode-infested soils before rehydration, but increased to high levels posthydration. Moisture effects were evident from the onset of each experiment, whereas the effect of soil temperature on nematode-induced insect mortality was delayed and nonsigniÞcant until 14 wk after the initiation of the third experiment.

Soil moisture effects on the activity of three entomopathogenic nematodes (Steinernematidae and Heterorhabditidae) isolated from Meghalaya, India

“…The results of present study are in agreement with Ganguly and Singh (2001) who observed that S. thermophilum can infect and multiply well on several pests of crops at a wide range of soil moisture (3-16% w/w) conditions. In a similar manner, our findings on the effect of soil moisture on establishment of S. glaseri are also in agreement with Grant and Villani (2003) who reported that, in general, the virulence of S. glaseri increases with soil moisture content in sandy loam soil. Also, Koppenhöfer et al (1995) in their study on the effect of different soil moistures on pathogenicity of S. carpocapsae and S. glaseri observed that considerable establishment of IJs of S. carpocapsae occurred at 4-5% moistures, however, nematodes establishment declined at the highest soil moisture studied (19%).…”

“…Of these, the moisture conditions have been recognized as one of the most important factors in the soil environment affecting survival, virulence and persistence of nematodes (Kaya 1990;Klein 1990, Curran 1993. For instance, nematodes may become dormant at very low soil moisture; on the other hand they may not be able to move freely at very high soil moistures (Grant and Villani 2003). In several studies, variability in efficacy of EPNs has often been found to be associated with soil moistures (Gaugler et al 1994;Koppenhöfer et al 1995).…”

“…Several studies have demonstrated that IJs of different EPNs differ in their ecological and behavioral traits with regard to their persistence and survival in the soil (Kaya 1990;Koppenhöfer et al 1995). Among these, the soil moisture is considered to be one of the most important variables that affect nematode performance and survival in the soil (Kaya 1990;Glazer 2002;Grant and Villani 2003). It has been found that the low soil moisture can adversely affect nematode activity and survival, but a considerable number of EPNs could survive some degree of dehydration if the drying process is gradual (Womersley 1987).…”

“…Rapid decline in soil moisture can occur in the upper soil layers, especially in sandy soils with little water retention capacity, and EPNs are very frequently isolated from such soils (Hara et al 1991;Strong et al 1996). It thus emerges from the foregoing account that soil moisture range in which IJs can be active may differ among different EPN species (Koppenhöfer et al 1995;Grant and Villani 2003). It is primarily due to these reasons that if EPNs are to be used as effective and predictable biocontrol agents, a precise knowledge of their moisture requirements is an essential pre-requisite to maximize their success in the fields.…”

Influence of drought on plant performance through changes in belowground tritrophic interactions

“…First, it can directly affect the performance of plants (Chaves, Maroco, & Pereira, 2003), root herbivores (Barnett & Johnson, 2013; Johnson et al., 2010), and natural enemies (Grant & Villani, 2003; Rohde, Moino, Da Silva, Carvalho, & Ferreira, 2010). Second, soil moisture can alter the performance of root herbivores and their natural enemies indirectly via changes in plant chemistry (Khan, Ulrichs, & Mewis, 2010; Vaughan, Block, Christensen, Allen, & Schmelz, 2017).…”